Can anyone tell me?

[alan potts]

I posted up an image before but didn't really get any feed back as to my problems. The 183MC or 071MC are correctly space at 37.5mm back focus on this scope, I have bought the correct spacers now.

Could the more knowledgeable on site have a look at the stars and tell me if they think it's,

1,  Guiding, the air was a bit turbulent last night as it was 21c and quickly dropped to 6c over the image time of 2 hours.

2, Spacing, if so too short or too long.

3, Poor focus, I still find it very hard to focus this scope, even though I really take my time, the sweet spot in so tiny.

This is 32x3min subs with Darks and flats at minus 5 with a 183MC on a 330mm Borg F4.3 scope driven by CEM 60 with SW ED guidescope and 290mini..

I realise it is not well processed and over sharpened but I did this purely to get help and hopefully highlight the problem area.

 

Many thanks,

Alan

[vlaiv]

You are right - being that much processed does not help with determining the cause of problems.

In fact - I'm not sure what exactly is your problem as having stars like this:

screams color aberration to me - but it could be just down to processing.  Btw, what filter did you use with this camera? You do know that 183mc is only AR coated and you need UV/IR cut filter with it? If you in fact used UV/IR cut filter with it and this issue with color is not down to processing - then you might want different UV/IR cut filter - something like L3 from astronomik.

Since you are mentioning distance of field flattener - I suspect you are actually concerned about star shapes in the corners?

In that case - I would suspect tilt as stars in bottom of the image are just fine, while stars on top have astigmatism to them:

Top of the image:

Cross / seagull shaped stars (although it is hard to tell due to level of processing)

Bottom of the image:

mostly round - but again, it's hard to tell

 

[Skipper Billy]

I am with Vlaiv on the tilt issue. If you can post the original unprocessed TIFF I will happily run it through CCD Inspector for you this evening which will confirm whether its tilt or curvature.

[alan potts]

Yes I did not pay too much attention to the processing and actually (wrongly it seems) though I was helping. I post here the tiff right out of DSS just reduced to 16 bit so it loads this week.

Vlaiv, I am using a L2 Astronmiks IR/UV filter which normally gives decent results on my APO but this is only an 77EDll two element Borg.

M43 32x 3mins 183mc.tif

 

Many thanks both of you.

Alan

[carastro]

Looks like there could be a bit of tilt/coma but with such overprocessed stars it is difficult to tell.

Just downloaded and will process and see what the result is.

Carole 

[carastro]

I just processed it.  

It does look like something is going on in the corners on the right side but not the left (In the orientation of the download and my process.

As the left side top seems OK to me and the bottom left OK (ish), I would suggest this is probably tilt though there could be another factor involved which I can;t quite fathom since the stars are elongated upright on the top right, but diagonally bottom right.

 

Edited February 2, 2020 by carastro

[symmetal]

Looking at the individual colour channels the red is significantly out of focus over the whole image compared to the green and blue. The green shows the best focus with the blue almost as good. Also on the right side of the image the green and blue channels are still pretty good with the elongated stars being caused by the red channel. As it's a OSC camera it would seem to be too much IR getting through. The L2 Astronomic filter has a wider passband compared to the L1 and may not be so suitable for this scope but I'm surprised it's causing this much blur on the red channel. 

Alan

[vlaiv]

9 minutes ago, symmetal said:

The L2 Astronomic filter has a wider passband compared to the L1

I was under the impression that it is other way around L1 being widest and L3 narrowest of the three:

In any case this scope would benefit from the narrowest of the three (L3 according to above graph).

[alan potts]

1 hour ago, carastro said:

I just processed it.  

It does look like something is going on in the corners on the right side but not the left (In the orientation of the download and my process.

As the left side top seems OK to me and the bottom left OK (ish), I would suggest this is probably tilt though there could be another factor involved which I can;t quite fathom since the stars are elongated upright on the top right, but diagonally bottom right.

 

Carole, Skipper and Vliav,

Don't feel you realise how much I depend on you lot and what a help you all are to me. Thanks for all you do, I always take what you say seriously, even if it looks like I don't. Carole you image looks so much better and very much like the one I got got second go, lord knows what I did with the one I posted

Confessions time, I have just notice a shinny chrome knob on the tube of the scope near to the focus, yes if I am honest I have seen it before but sort of forgot about it completely. When you tighten this it does move the back part of the tube a couple of millimeters or so which is sagging with the weight of the camera and cables. After tighten. post focus I have to say the stars look so much better and pretty much round, its difficult to tell on the readouts from APT but look OK. I still find this helical focus system a difficult one to use, or is it just APT making it difficult as I only get an image every second.

I think crabby processing aside you have helped me find my answers.  With the clear skies I get I should be telling you lot how to do things I get so much time outside, maybe one day.

Thanks all,

Alan

Alan

[alan potts]

11 minutes ago, vlaiv said:

I was under the impression that it is other way around L1 being widest and L3 narrowest of the three:

In any case this scope would benefit from the narrowest of the three (L3 according to above graph).

I only have 2xL2 which when I think about was a bit stupid, this is a Borg so should be a quality objective, L1 is for high end APO's like Tak's etc I settled for the middle ground. Thanks for the help read the last post of mine in answer to Carole, something I missed.

Alan

[vlaiv]

1 minute ago, alan potts said:

I only have 2xL2 which when I think about was a bit stupid, this is a Borg so should be a quality objective, L1 is for high end APO's like Tak's etc I settled for the middle ground. Thanks for the help read the last post of mine in answer to Carole, something I missed.

Alan

That Borg is rather fast at F/4.3 and even triplet would struggle with color correction at that F/ratio so no wonder that double shows a bit of unfocused light. L3 could help, but not sure how much.

In any case - this is one of the reasons you are struggling with focus - fast scopes have very thin critical focus zone and it is rather hard to get good focus - although your image seems to have that aspect covered, I have not seen any focus issues (even in fast dropping temperatures).

[alan potts]

27 minutes ago, symmetal said:

Looking at the individual colour channels the red is significantly out of focus over the whole image compared to the green and blue. The green shows the best focus with the blue almost as good. Also on the right side of the image the green and blue channels are still pretty good with the elongated stars being caused by the red channel. As it's a OSC camera it would seem to be too much IR getting through. The L2 Astronomic filter has a wider passband compared to the L1 and may not be so suitable for this scope but I'm surprised it's causing this much blur on the red channel. 

Alan

Maybe I was seduced by it being a Borg scope, which I was of the opinion was a quality objective even though it is only an ED 2 element. L1 is for the highest end scopes I believe so I think you mean L3, which ever way I can check. I have found something else I was not doing by way of tighening the focus lock, this lifts the camera slightly from the free-focus position, I dare say this will have had an effect.

Alan

[alan potts]

6 minutes ago, vlaiv said:

That Borg is rather fast at F/4.3 and even triplet would struggle with color correction at that F/ratio so no wonder that double shows a bit of unfocused light. L3 could help, but not sure how much.

In any case - this is one of the reasons you are struggling with focus - fast scopes have very thin critical focus zone and it is rather hard to get good focus - although your image seems to have that aspect covered, I have not seen any focus issues (even in fast dropping temperatures).

The time I try to take to get focus is unreal, I see now just how tiny the sweet spot is. I may well invest in another filter, can't believe I bought two the same how daft. The L2 works fine on the 805mm apo but then that's F7 and decent quality so maybe should. I really value your input, don't always understand it all but I always read your posts.

Alan

[Skipper Billy]

@alan potts

These are the results of your image from CCD Inspector in 2D and 3D.

There is tild from top left to bottom right which will make focusing all 3 colours across the entire chip a bit of a challenge on a fast scope.

There is also some curvature as seen in the 3D plot.

I did a quick and dirty process and got a similar result to Carole.

Hope that helps!

David (aka Skipper Billy)

 

[Skipper Billy]

This is my quick and dirty - I don't have the light touch elegance that Carole has ! 😉 

 

[symmetal]

1 hour ago, vlaiv said:

I was under the impression that it is other way around L1 being widest and L3 narrowest of the three:

In any case this scope would benefit from the narrowest of the three (L3 according to above graph).

Yes, you're right, I meant to put L3 

I don't think CCDI is so useful with OSC cameras. Here's the results on the separate R, G and B channels along with the composite. Note the large differences in tilt and curvature (and in different directions) depending on what colour you're looking at.

Alan

Edited February 2, 2020 by symmetal

[Skipper Billy]

16 minutes ago, symmetal said:

I don't think CCDI is so useful with OSC cameras. Here's the results on the separate R, G and B channels along with the composite. Note the large differences in tilt and curvature (and in different directions) depending on what colour you're looking at.

Well I have learnt something there!

[symmetal]

Actually, thinking again, the CCDI results could be seen as more useful  with OSC in that they do show where your focus problems are for each colour which you couldn't do if it was a mono camera with a Luminance filter. This would just give effectively the composite image as Billy posted and you may try correcting tilt etc. when it's seems to be primarily a Red focus problem.

Alan

[alan potts]

11 hours ago, Skipper Billy said:

Well I have learnt something there!

 

11 hours ago, symmetal said:

Actually, thinking again, the CCDI results could be seen as more useful  with OSC in that they do show where your focus problems are for each colour which you couldn't do if it was a mono camera with a Luminance filter. This would just give effectively the composite image as Billy posted and you may try correcting tilt etc. when it's seems to be primarily a Red focus problem.

Alan

Look if it is OK, Dave and Alan, thanks for effort you both have put in, can I post a tiff for you both (maybe here and message you both) where I have now tighten up the focus lock, this clearly and visually had an effect on the plain of the rear part of the reducer. My feelings are this could well be causing the lions share of any problems. Though it is not so easy to see changes on my screen stars did look round again, though maybe still not the sharp focus that it could be (maybe this is the filter's weakness causing this)

I did get out last night to try things but the gap in the clouds was small and I rushed things and got poor focus, it was good enough however to see there was a dramatic improvement in star shape and general colour. I don't think the Tiff file would be good enough for the same treatment that you put the other file through but will upload if you wish, it is only 14x3mins so not wonderful.

What happened was where I sit in the obsey I cannot see this knob which locks everything up nice and tight, also straightens things up. I simply forgot about it the last few weeks and this is when results have been poor, I have to say the same problem was not so obvious when I used the 071. I will also consider the L3 filter at a later date when I am hoping to buy one of FLO new apo's, maybe the 85mm.

Alan

[symmetal]

Yes, no problem Alan  Hopefully your focus lock has improved things.

Alan

[Skipper Billy]

Ditto - fire away

 

[Skipper Billy]

.

[alan potts]

15 hours ago, symmetal said:

Yes, no problem Alan  Hopefully your focus lock has improved things.

Alan

I never realised that F4.3 even on a refractor was so difficult, the tiniest bit out seems like a mile. Judging by the blurred shot from the other night stars at least look round and seems to have lost that redness. Maybe the L2 filter will do the job which is the same one I had in place when using the scope with the 071mc , the results from that couple of weeks were much better but the FOV is much larger, however there was still that mis-shaping at the edges which was before I got the correct spacer tube, 1mm seems to make a massive difference.

11 hours ago, Skipper Billy said:

Ditto - fire away

 

Now all we need is the clear skies I have had for past week, looks like the weather has taken a down turn which with the Moon getting bigger is a good thing I guess. Soon as I get something I will post it here, thank you both of you for what you have done.

Alan

[symmetal]

Just to clarify the 3D plots from CCD Inspector. The R and B seem to show the curvature in opposite directions but they may actually be in the same direction. It's probably more likely they are in the same direction. CCDI has no way of knowing whether the out of focus/shape stars are in front of, or behind the plane of focus so it just displays these poorer stars in the 'up' Z direction, the worse the star the higher value of Z.

For each plot the best focus stars are given the lowest Z value and all other stars are plotted as having a higher Z value. If the best stars are in the centre the curvature will generally be a 'bowl' shape like the B image above. If the best stars are towards the edges the curvature will generally be a 'dome' shape like the R or composite image above.

The colours used (black to pink) are relative indicators for that plot only. So a pink area in one plot doesn't mean it's as bad as a pink area in another plot. All the images shown go from black (good) to pink (bad), but the Green channel 'bad' is a lot better than the Red channel 'bad'. 

I believe the curvature and 3D plots just take the star FWHM values. If you look at just the Red channel on Alan's image the stars are very elongated on the right hand side but CCDI gives these the best 'scores' on the curvature, and 3D plots (lowest Z value) while the circular but out of focus stars nearer the centre are given a poor score (high Z value).

If you view the star aspect ratio plot as shown below it does show the Red channel as being worse on the right so in reality all the various plots have to be looked at to show what's actually happening and not just rely on one plot.

CCDI displays problems as percentages with the higher the percentage the worse the problem, but a percentage of what I don't kinow. What does 100% curvature, tilt or aspect look like. 

Alan

 

[alan potts]

On 04/02/2020 at 20:29, symmetal said:

Just to clarify the 3D plots from CCD Inspector. The R and B seem to show the curvature in opposite directions but they may actually be in the same direction. It's probably more likely they are in the same direction. CCDI has no way of knowing whether the out of focus/shape stars are in front of, or behind the plane of focus so it just displays these poorer stars in the 'up' Z direction, the worse the star the higher value of Z.

For each plot the best focus stars are given the lowest Z value and all other stars are plotted as having a higher Z value. If the best stars are in the centre the curvature will generally be a 'bowl' shape like the B image above. If the best stars are towards the edges the curvature will generally be a 'dome' shape like the R or composite image above.

The colours used (black to pink) are relative indicators for that plot only. So a pink area in one plot doesn't mean it's as bad as a pink area in another plot. All the images shown go from black (good) to pink (bad), but the Green channel 'bad' is a lot better than the Red channel 'bad'. 

I believe the curvature and 3D plots just take the star FWHM values. If you look at just the Red channel on Alan's image the stars are very elongated on the right hand side but CCDI gives these the best 'scores' on the curvature, and 3D plots (lowest Z value) while the circular but out of focus stars nearer the centre are given a poor score (high Z value).

If you view the star aspect ratio plot as shown below it does show the Red channel as being worse on the right so in reality all the various plots have to be looked at to show what's actually happening and not just rely on one plot.

CCDI displays problems as percentages with the higher the percentage the worse the problem, but a percentage of what I don't kinow. What does 100% curvature, tilt or aspect look like. 

Alan

 

 

On 03/02/2020 at 19:28, Skipper Billy said:

.

Alan and Dave,

I don't know if you can assess this it is only 3 frames stacked that I got the other night, I now have 70cms of snow outside and it could well be some time before I can get the Obsey open. Golly it was clear last night, no power and utterly Black sky before they got some power back on, 24hrs we were off, lots of damage all around.

So I have loaded this on the off chance it will do, I think it is reasonable focus but that really causes me problems with so short a scope. To me the stars look better.

Autosave.tif

 

Hope you have some joy.

Alan from a very snowy Bulgaria.